1. Field of the Invention
The invention relates to an optical recording medium capable of recording data thereinto or reproducing data therefrom, and more particularly to an optical recording medium suitable for carrying out so-called xe2x80x9csimultaneous recording and verificationxe2x80x9d where confirmation as to whether data is properly recorded is carried out concurrently with recording data into a medium. The invention also relates to a method of optically recording data into an optical recording medium and reproducing data therefrom.
2. Description of the Related Art
As one of optical disc mediums capable of recording data thereinto and reproducing data therefrom both by radiating laser beam spot thereto is known a phase-change type optical disc. The phase-change type optical disc is capable of carrying out over-recording by a single beam, which is difficult to carry out by a magneto-optical (MO) disc. An optical head system for the phase-change optical disc is simpler than that for the MO disc.
A method of carrying out simultaneous recording and verification in such a phase-change type recording medium has been suggested in Japanese Unexamined Patent Publications Nos. 60-145537, 63-183624, and 6-349067. According to these Publications, when pulse beams are radiated onto the phase-change type recording medium, an intensity of reflected beams is varied almost at the same with the radiation. The suggested methods make it possible to confirm whether data is properly recorded by detecting the variation in the reflected beams by means of either the reflected beams itself or RF signals.
Roughly speaking, data is recorded into a phase-change type optical disc medium by the following steps: radiating laser beams onto a non-recorded region, which is in crystal condition, to thereby heat a recording layer; a temperature of the recording layer being raised; melting of the recording layer; and cooling down the recording layer to thereby reduce the recording layer amorphous. Hence, non-recorded and recorded regions have different phase conditions, and as a result, non-recorded and recorded regions have different reflectivity. Accordingly, an intensity of reflected laser beams is varied in accordance with the phase condition. A phase-change type optical disc medium utilizes such variation in an intensity of reflected laser beams for recording data thereinto.
It is known that a recording layer becomes as illustrated in FIG. 1, when a recording layer is molten by a laser beam spot. Thus, all regions of a recording layer are not always molten in a beam spot, even if a laser beam is radiated onto the recording layer. Herein, the molten region 60 corresponds to a region in which data is recorded, and the non-molten region 62 corresponds to a region in which data is not recorded yet. As mentioned earlier, the molten region 60 becomes amorphous when cooled down, whereas the non-molten region 62 remains crystal. If a recording layer is not molten, the recording layer is not reduced amorphous. In the beam spot, reflectivity of the recorded or amorphous region 60 coexists together with reflectivity of the non-recorded or crystal region 62, and hence it would be quite difficult to clearly distinguish the recorded region 60 from the non-recorded region 62. As a result, it would be difficult to accurately carry out simultaneous recording and verification only based on variation in the reflectivity. Hence, verification has to be carried out again after data has been recorded into a phase-change type optical disc medium in the above mentioned conventional mediums. As a result, it is substantially impossible to carry out simultaneous recording and verification in the conventional mediums.
In addition, in the conventional mediums where the recorded region has to have reflectivity quite different from that of the non-recorded region, there would be generated a large fluctuation in RF signals in over-recording, resulting in unstable verification together with reduction in reliability.
In view of the foregoing problems of the conventional recording mediums, it is an object of the present invention to provide a phase-change type optical recording medium which is capable of accurately carrying out simultaneous recording and verification, specifically carrying out verification by which it is confirmed whether data is properly recorded both in initial recording and over-recording.
Another object of the present invention is to provide a phase-change type optical recording medium which is capable of carrying out verification with high accuracy in smaller period of time to thereby make it possible to record data with higher reliability.
It is also an object of the present invention to provide a method of optically recording data by employing the above mentioned phase-change type optical recording medium.
In one aspect, there is provided a phase-change type optical recording medium, including (a) a substrate, (b) a recording layer formed on the substrate, phase condition of the recording layer being changed when a laser beam is radiated thereonto, to thereby record, erase or reproduce data into or from the recording layer, and (c) a reflection layer formed on the recording layer for reflecting a laser beam having been radiated onto the recording layer. The recording layer is formed so that the following equation (A) is established:
Rc greater than Rm greater than Raxe2x80x83xe2x80x83(A)
wherein Rc indicates a reflectivity to be obtained when the recording layer is in crystal condition, Ra indicates a reflectivity to be obtained when the recording layer is in amorphous condition, and Rm indicates a reflectivity to be obtained when the recording layer is in mixed condition of molten condition and crystal or amorphous condition.
By arranging the recording layer to have a thickness such that the above mentioned equation (A) is established, it is possible to have recording sensitivity suitable for recording data into and reproduce data from an optical recording medium, and accomplish simultaneous recording and verification. In addition, the phase-change type optical recording medium is capable of providing high reproducing output, being accessible at a higher speed, and recording data at a higher density.
There is further provided a phase-change type optical recording medium, including (a) a substrate, (b) a recording layer formed on the substrate, phase condition of the recording layer being changed when a laser beam is radiated thereonto, to thereby record, erase or reproduce data into or from the recording layer, and (c) a reflection layer formed on the recording layer for reflecting a laser beam having been radiated onto the recording layer. The recording layer is formed so that the following equation (B) is established:
|Rcxe2x88x92Ra|xe2x89xa65%
Rc greater than Rm, Ra greater than Rmxe2x80x83xe2x80x83(B)
wherein Rc indicates a reflectivity to be obtained when the recording layer is in crystal condition, Ra indicates a reflectivity to be obtained when the recording layer is in amorphous condition, and Rm indicates a reflectivity to be obtained when the recording layer is in mixed condition of molten condition and crystal or amorphous condition.
Since the above mentioned equation (B) includes reflectivity in the laser beam spot as one of standards for judgement, it is surely confirmed as to whether the recording layer has a molten or recorded region in the laser beam spot by means of the phase-change type optical recording medium meeting the equation (B). Thus, it is possible to carry out verification while data is being recorded into the phase-change type optical recording medium.
For instance, if verification is to be carried out by employing RF signals obtained from reflected laser beams, it would be possible to obtain clearly distinguishable RF waveforms between when data is properly recorded and when data is not properly recorded. In addition, since RF waveforms obtained when data is properly recorded is stable, precise verification can be carried out. Furthermore, since a difference between Rc and Ra is arranged within 5% and Rm is arranged smaller than Rc and Ra, it would be possible to have the same RF waveforms even in over-recording as the waveforms obtained in initial recording, which ensures that accurate verification can be carried out similarly to verification in initial recording.
It would be possible to accurately carry out verification also by analyzing RF waveforms obtained immediately after a certain region of a recording layer in the laser beam spot commences to be molten. According to this mode of verification, a period of time necessary for verification can be shortened, and data can be recorded in initial recording or over-recording without reduction in transfer speed with higher reliability.
The above-mentioned equations (A) and (B) may be established in various ways. For instance, the substrate and recording layer may be designed to have a thickness so that the equation (A) or (B) is established. As an alternative, the substrate and recording layer may be made of particular material so that the equation (A) or (B) is established.
The phase-change type optical recording medium may further include a lower protection layer formed between the substrate and the recording layer, and an upper protection layer formed between the recording layer and the reflection layer, in which case the substrate, recording layer, lower protection layer and upper protection layer may be designed to have a thickness so that the equation (A) or (B) is established. As an alternative, the substrate, recording layer, lower protection layer and upper protection layer may be made of particular material so that the equation (A) or (B) is established.
A laser beam may be radiated to the phase-change type optical recording medium in any directions. However, it is preferable that a laser beam is radiated through the substrate for the purpose of simplification of a driver optical system and reduction of a recording apparatus in size.
The recording layer may be made of at least germanium (Ge), antimony (Sb) or tellurium (Te). The lower and upper protection layers may be made of any material suitable for optically recording medium. For instance, it is preferable that the lower and upper protection layers include ZnSSiO2, SiN, SiO, SiO2, TaO2 or SiAlON. The reflecting layer may be made of any material suitable for optically recording medium. For instance, it is preferable that the reflecting layer includes Al, Ti, Ta, Cu, Au or Si as principal ingredient.
The phase-change type optical recording medium may further include additional layers. For instance, the phase-change type optical recording medium may further include an UV resin protection layer formed on the reflection layer. As an alternative, the phase-change type optical recording medium may further include an intermediate layer between the IN resin protection layer and the reflection layer, which intermediate layer is made of the same material as that of the lower protection layer. In the phase-change type optical recording medium, the reflection layer is required to have a thickness through which a laser beam can pass. The provision of the intermediate layer enhances designability in the phase-change type optical recording medium.
In the present invention, verification is carried out with higher accuracy by arranging a difference between Rc and Ra at a wavelength of a laser beam used for recording data to be within 5%. Hence, if a laser beam having a certain wavelength were commonly employed for both recording and reproducing data, it would not be possible to have a preferred C/N ratio by a difference between Rc and Ra. Thus, in order to have a preferred C/N ratio, the optical recording medium may be constructed so that a difference between Rc and Ra necessary for reproducing data having been recorded in the medium is able to be obtained by a wavelength for reproducing data. However, it is preferable that crystal and amorphous regions formed in the recording layer have a phase difference, in order that a common wavelength can be employed for both recording and reproducing data. It is preferable that a phase difference xcfx86 between crystal and amorphous regions both formed in the recording layer at a laser wavelength used for recording data meet the following equation (C).
30xc2x0xe2x89xa6|xcfx86|xe2x89xa6180xc2x0xe2x80x83xe2x80x83(C)
The equation (C) may be established in various ways. For instance, the layers constituting the phase-change type optical recording medium may be designed to have a thickness or be made of particular material such that the equation (C) is established.
The phase-change type optical recording medium may be fabricated by means of conventional processes such as sputtering.
In another aspect, there is provided a method of optically recording data, including the steps of (a) preparing a phase-change type optical recording medium, the phase-change type optical recording medium comprising: a substrate; a recording layer formed on the substrate, phase condition of the recording layer being changed when a laser beam is radiated thereonto, to thereby record, erase or reproduce data into or from the recording layer; and a reflection layer formed on the recording layer for reflecting a laser beam having been radiated onto the recording layer, the recording layer being formed so that the following equation (A) is established:
Rc greater than Rm greater than Raxe2x80x83xe2x80x83(A)
wherein Rc indicates a reflectivity to be obtained when the recording layer is in crystal condition, Ra indicates a reflectivity to be obtained when the recording layer is in amorphous condition, and Rm indicates a reflectivity to be obtained when the recording layer is in mixed condition of molten condition and crystal or amorphous condition, (b) radiating laser beam onto the recording layer, (c) monitoring laser beam reflected from the recording layer, and (d) judging whether data is properly recorded, based on how the reflected laser beam varies in an amount.
When laser beam having a predetermined intensity is radiated onto the recording layer, data may be judged to be properly recorded, if the reflected beam is suddenly reduced in an amount immediately after radiation of the laser beam.
There is further provided a method of optically recording data, including the steps of (a) preparing a phase-change type optical recording medium, the phase-change type optical recording medium comprising: a substrate; a recording layer formed on the substrate, phase condition of the recording layer being changed when a laser beam is radiated thereonto, to thereby record, erase or reproduce data into or from the recording layer; and a reflection layer formed on the recording layer for reflecting a laser beam having been radiated onto the recording layer, the recording layer being formed so that the following equation (B) is established:
|Rcxe2x88x92Ra|xe2x89xa65%
Rc greater than Rm, Ra greater than Rmxe2x80x83xe2x80x83(B)
wherein Rc indicates a reflectivity to be obtained when the recording layer is in crystal condition, Ra indicates a reflectivity to be obtained when the recording layer is in amorphous condition, and Rm indicates a reflectivity to be obtained when the recording layer is in mixed condition of molten condition and crystal or amorphous condition, (b) radiating laser beam onto the recording layer, (c) monitoring laser beam reflected from the recording layer, and (d) judging whether data is properly recorded, based on how the reflected laser beam varies in an amount.
It is preferable that the laser beam is radiated in pulse.
The above and other objects and advantageous features of the present invention will be made apparent from the following description made with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the drawings.